I took this photo while working on the "Micro-Crystals" video, and thought this might be a challenge. What common chemical is this? Hint: The colors are from polarizing filters. The crystals are normally clear.
These are sugar crystals, seen through a microscope at 40X magnification, with polarized filters. The polarized filters cause the colors through a process called birefringence. Without the filters, the crystals are clear.
The Growing Crystals Under the Microscope video includes some video of the sugar crystals, as well as other crystals growing.